1. Field of the Invention
This invention relates to a video signal recording apparatus, and in particular, is directed to an apparatus for recording the video signal on a magnetic tape which is stopped or moved at slow speed.
2. Description of the Prior Art
In a VTR (video tape recorder), so far it has been requested that a tape speed can freely be varied so as to reproduce a slow or fast motion picture and the like as desired. For this, many improvements had been made and above all, the present inventors had previously proposed a dynamic tracking technique. In accordance with this dynamic tracking technique, it is possible that different speed reproductions are carried out at any desired different tape speeds to reproduce various different speed picture images.
However, considering the freedom at the recording side of the VTR, the recording side has almost no freedom in its time operation at present. For example, when some short recording portions are individually recorded and then composed or edited to one another to form a record tape on which the video signal is successively recorded, only the electronic edition technique for the VTR, namely, assemble and insert techniques are employed to cope with such recording. Naturally, the above technique requires complicated and troublesome procedures such as preroll, synchronization, framing (servo lock), review (check-playback) and so on.
More specifically, when a video signal of, for example, only one frame is required to record, it is necessary that a magnetic tape of the tape length exceeding several seconds is reciprocated, thus the mechanical stress against the magnetic tape being increased or the time loss beyond 10 seconds being caused. Under this restriction, when it is required that the video signal is recorded at every desired frame and the frame recording is composed for 10 seconds, the magnetic tape suffers the passing stress more than 600 times and a recording time of about 2 hours is necessary at present, assuming that the color frame synchronizing time and the minimum preroll time of the VTR are respectively selected as 5 seconds.
A further defect is that when the recording command is issued to record predetermined portion of the video signal, the VTR can not enter into the recording mode immediately but takes several seconds to several ten seconds. As a result, it is no exaggeration to say that a real time recording can hardly be performed.
Accordingly, it is very troublesome to use the for manufacturing a master tape of a video disc which is recently put into practical use, for recording an animation picture and a still picture file.
On the other hand, there has been already proposed different kinds of VTRs for the above purpose, wherein even if the quality of the recorded picture image is very poor, a video signal is recorded on the tape at a special tape speed and a special recording timing. One of the type of VTRs is provided with a rapid tape drive recording system which has been used once in a portaboe VTR for home use. According to the recording system, a similar recording pattern to the ordinary pattern will be obtained, if it is not necessary to take into consideration of synchronization and address identification. In this VTR, when the recording command is issued, a rotary capstan is instantly made in close contact with the tape to rapidly raise the tape speed to a standard tape speed, whereby the video signal is immediately recorded on the tape.
However, due to the tension fluctuation and speed fluctation of the tape, this type of VTR is unable to carry out the recording with high accuracy and is not free from the dropout of picture image, phase deviation, deterioration of picture quality and so on. Therefore, it is known that this VTR is only used for the simple type.
Another system is well-known as a so-called surveillance type of VTR. In the type of VTR a capstan is driven by a step motor to intermittently move a tape to thereby carry out the intermittent recording thereon. At that time, the angle of the tape around the drum is corrected by means of a movable tape guide or changing an inclination drum shaft.
However, since this system is difficult to keep its mechanical or constructive accuracy, the pattern of the slant track can not be made completely equivalent to that of the slant track which is formed at standard tape speed.
However, as far as the surveillance type of the VTR is concerned, it is sufficient that a picture image can be reproduced and viewed particularly when an abnormal phenomenon occurs in the observation. Therefore, the quality of the picture is of no importance in most case.